Ground water atlas of the United States: Segment 13, Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands
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Alaska, Hawaii, Puerto Rico, Virgin Islands↗
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Major geohydrologic units in and adjacent to the Ozark Plateaus province, Missouri, Arkansas, Kansas, and Oklahoma
An investigation of the geohydrologic system in the Ozark Plateaus province (index map and Fenneman, 1938) has been made as part of the Central Midwest Regional Aquifer System Analysis (Jorgensen and Signor, 1981), a major study of the regional aquifer system in parts of 10 States. The study is one of several by the U.S. Geological Survey that are designed to increase knowledge of the flow regime and geohydrologic properties of regional aquifer systems in the United States. Because a large quantity of fresh ground water is available in aquifers underlying the Ozark Plateaus province, a subregional project has been established to study the geohydrologic units of this area in more detail than is practical in the regional study. The stratigraphic and geologic relationships among the primary geohydrologic units in and adjacent to the Ozark Plateaus is depicted in this atlas (Chapter A). This is the first of a series of chapters (A-H) that includes maps of the altitude of the top, thickness, potentiometric surface, and percentage-of-shale content of individual geohydrologic units.
Arkansas, Kansas, Missouri, Oklahoma↗
Atlas of water resources in the Black Hills area, South Dakota
The Black Hills area is an important resource center that provides an economic base for western South Dakota through tourism, agriculture, the timber industry, and mineral resources. In addition, water originating from the area is used for municipal, industrial, agricultural, and recreational purposes throughout much of western South Dakota. The Black Hills area also is an important recharge area for aquifers in the northern Great Plains. Population growth, resource development, and periodic droughts have the potential to affect the quantity, quality, and availability of water within the Black Hills area. Growth has resulted in competing interests for available water supplies. The Black Hills Hydrology Study was initiated in 1990 to address these concerns. This long-term study is a cooperative effort between the U.S. Geological Survey (USGS), the South Dakota Department of Environment and Natural Resources, and the West Dakota Water Development District, which represents various local and county cooperators.
Hydrologic Atlas↗
Stream composition of the conterminous United States
This atlas is comprise of three maps of the conterminous United States which show separately the prevalent dissolved-solids concentrations, prevalent chemical type, and average sediment concentration of rivers. The river-composition data shown on plates 1-3 provide a starting point for evaluating our surface-water resources on a nationwide scale, indicate regions where acceptable supplies might be found and delineate some of the principal trouble spots throughout the country.
Hydrologic Atlas↗
Backwater at bridges and densely wooded flood plains, Thompson Creek near Clara, Mississippi
Floodflow data that will provide a base for evaluating digital models relating to open-channel flow were obtained at 22 sites on streams in Alabama, Louisiana, and Mississippi. Thirty-five floods were measured. Analysis of the data indicated methods currently in use would be inaccurate where densely vegetated flood plains are crossed by highway embankments and single-opening bridges. This atlas presents flood information at the site on Thompson Creek near Clara, MS: Water depths, velocities, and discharges through bridge openings on Thompson Creek near Clara, MS, for flood of March 3, 1971, are shown, together with peak water-surface elevations along embankments and along cross sections. Manning 's roughness coefficient values in different parts of the flood plain are shown on maps, and flood-frequency relations are shown on a graph. (USGS).
Hydrologic Atlas↗
Ground Water Atlas of the United States: Segment 6, Alabama, Florida, Georgia, South Carolina
The four States-Alabama, Florida, Georgia, and South Carolina-that comprise Segment 6 of this Atlas are located adjacent to the Atlantic Ocean or the Gulf of Mexico, or both. These States are drained by numerous rivers and streams, the largest being the Tombigbee, Alabama, Chattahoochee, Suwannee, St. Johns, Altamaha, and Savannah Rivers. These large rivers and their tributaries supply water to cities such as Columbia, S.C., Atlanta, Ga., and Birmingham, Ala. However, the majority of the population, particularly in the Coastal Plain which comprises more than one-half of the four-State area, depends on ground water as a source of water supply. The aquifers that contain the water are mostly composed of consolidated to unconsolidated sedimentary rocks, but also include hard, crystalline rocks in parts of three of the States. This chapter describes the geology and hydrology of each of the principal aquifers throughout the four-State area. Precipitation is the source of all the water in the four States of Segment 6. Average annual precipitation (1951-80) ranges from about 48 inches per year over a large part of central South Carolina and Georgia to about 80 inches per year in mountainous areas of northeastern Georgia and western South Carolina. (fig. 1) In general, precipitation is greatest in the mountains (because of their orographic effect) and near the coast, where water vapor, which has been evaporated primarily from the ocean and the gulf, is picked up by prevailing winds and subsequently condenses and falls as precipitation when reaching the shoreline. Much of the precipitation either flows directly into rivers and stream as overland runoff or indirectly as baseflow discharging from aquifers where the water has been stored for a short time. Accordingly, the areal distribution of average annual runoff from 1951 to 1980 (fig. 2) directly reflects that of average annual precipitation during the same period: runoff is greater in mountainous areas and near the coast. Average annual runoff in the four-State area ranges from about 8 inches per year in parts of north-central Florida to about 50 inches per year in the mountains of northeastern Georgia. Comparison of the precipitation and runoff maps shows precipitation is greater than runoff everywhere in the four-State area. Much of the precipitation that falls on the area is returned to the atmosphere by evapotranspiration-evaporation from surface-water bodies, such as lakes and marshes, and transpiration from plants. However, a substantial part of the precipitation is available for aquifer recharge throughout the area.
Alabama, Florida, Georgia, South Carolina↗
Backwater at bridges and densely wooded flood plains, west fork Amite River near Liberty, Mississippi
Floodflow data that will provide a base for evaluating digital models relating to open-channel flow were obtained at 22 sites on streams in Alabama, Louisiana, and Mississippi. Thirty-five floods were measured. Analysis of the data indicated methods currently in use would be inaccurate where densely vegetated flood plains are crossed by highway embankments and single-opening bridges. This atlas presents flood information at the site on West Fork Amite River near Liberty, MS. Water depths , velocities, and discharges through bridge openings on West Fork Amite River near Liberty, MS for floods of December 6, 1971 , and March 25, 1973, are shown, together with peak water-surface elevations along embankments and along cross sections. Manning 's roughness coefficient values in different parts of the flood plain are shown on maps, and flood-frequency relations are shown on a graph. (USGS).
Hydrologic Atlas↗
Backwater at bridges and densely wooded flood plains, Yockanookany River near Thomastown, Mississippi
Floodflow data that will provide a base for evaluating digital models relating to open-channel flow were obtained at 22 sites on streams in Alabama, Louisiana, and Mississippi. Thirty-five floods were measured. Analysis of the data indicated methods currently in use would be inaccurate where densely vegetated flood plains are crossed by highway embankments and single-opening bridges. This atlas presents flood information at the site on Yockanookany River near Thomastown, Miss. Water depths, velocities, and discharges through bridge openings on Yockanookany River near Thomastown, Miss., for floods of April 12, 1969, January 2, 1970, and March 15, 1975, are shown, together with peak water-surface elevations along embankments and along cross sections. Manning 's roughness coefficient values in different parts of the flood plain are shown on maps, and flood-frequency relations are shown on a graph. (Kosco-USGS)
Hydrologic Atlas↗
Preliminary map of the conterminous United States showing depth to and quality of shallowest ground water containing more than 1,000 parts per million dissolved solids
In this atlas, mineralized ground water is viewed presently as a source of water in some areas, but in much of the country as a source for future development. Mineralized water underlies large areas of the country, and its importance will grow as present supplies of fresh water are appropriated and developed. The potential uses fall in two main categories: (1) direct use in industrial processes, such as cooling, or for irrigation, where a moderate mineral content may not be a disadvantage; and (2) use after demineralization or dilution to whatever degree may be required by the intended user. It is clearly more efficient to produce and process water of moderate mineralization at points of use, where available in adequate amounts, than it is to process ocean water and pump it many miles from the sea. The Geological Survey, as a part of its responsibility to describe the water resources of the United States, has surveyed the known occurrences of mineralized ground water in the conterminous United States. The results are shown on the maps (sheets 1 and 2). This atlas was prepared to meet needs for information on the distribution and availability of mineralized water as expressed by Government agencies, private industries, and consultants. The maps are one step in providing an inventory of mineralized water of the Nation and will serve as a planning guide for further investigations and for development. They are necessarily generalized in many places owing to the complexity of the occurrence of the mineralized water, lack of detailed information for parts of the nation, and the difficulties inherent in attempts to put three-dimensional information on maps.
Hydrologic Atlas↗
Geohydrologic maps of the Potomac-Raritan-Magothy aquifer system in the New Jersey Coastal Plain
The Potomac Group and the Raritan and Magothy Formations of late Early to early Late Cretaceous age form an aquifer system consisting chiefly of interlayered beds of quartz sand, silt, and clay. The aquifer system is the most heavily pumped in New Jersey and contains fresh water over an area of about 2,500 sq mi. This atlas illustrates some of the geohydrologic information available for the aquifer system and its confining units. The maps show the configuration of the bedrock surface and the altitude of the top of the confining unit above the aquifer system. Also included are maps depicting the altitude of the top of the aquifer system, three time-related potentiometric surface configurations, and three head declines of the aquifer system. The area represented by these maps lies within the Coastal Plain physiographic province (Fenneman, 1938) and is almost entirely within New Jersey. The area is a low lying, gently rolling plain that ranges in altitude from sea level to about 390 ft. (Woodard-USGS)
New Jersey↗
Preliminary maps showing ground-water resources in the Lower Colorado River region, Arizona, Nevada, New Mexico, and Utah
This atlas was prepared to meet the need for information on the areal distribution, quantity, and availability of ground water in the lower Colorado River region, an area of about 140,000 square miles in parts of Arizona, Nevada, New Mexico, and Utah. The maps are necessarily generalized in places owing to the lack of sufficient data. In general the geohydrologic information pertains to large areas, and local exceptions occur. Users needing more detailed information for specific areas may address inquiries to the district chief of the U.S. Geological Survey at the addresses given in the section “Selected References.” The maps were prepared using data from previously published reports, data collected by other Federal State, and local agencies, and data from the files of the U.S. Geological Survey offices in Arizona, Nevada, New Mexico, and Utah. The report is the result of the lower Colorado River region Type I framework study made in cooperation with the U.S. Bureau of Reclamation.
Arizona, Nevada, New Mexico, Utah↗
Water resources of Wisconsin: Rock-Fox River basin
PURPOSE AND SCOPE The purpose of this report is to describe the physical environment, availability, distribution, characteristics, movement, quality, water problems, and use of water within the Rock-Fox River basin in order to aid in planning future water management within the basin. This report presents general information on the basin that was derived from data obtained from Federal, State, and local agencies. In addition, new data were collected from areas where available data were scarce. The reader is referred to the section entitled “Agencies Having Additional Information” and to the list of selected references (sheet 4) for sources of more detailed information. This atlas is one of a series of 12 river-basin studies designed to describe in general terms the water resources of the State. More detailed studies of problem areas will be required in the future as the need for additional information increases. LOCATION AND EXTENT The Rock-Fox River basin in Wisconsin, covers about 4,750 square miles in the southeastern part of the State. It includes all or parts of the following 13 counties: Columbia, Dane, Dodge, Fond du Lac, Green Lake, Jefferson, Kenosha, Milwaukee, Racine, Rock, Walworth, Washington, and Waukesha. It includes the area drained by the Rock, Fox, and Des Plaines Rivers within the State of Wisconsin. Although the basin boundary is the topographic divide, part of the streamflow is derived from ground water that drains from an area similar to, but not having the same boundaries as, the topographic basin. The ground-water basin covers about 4,350 square miles, 400 square miles less than the topographic basin. Most of the reduction in basin area is along the eastern side of the basin.
Wisconsin↗
Ground Water Atlas of the United States: Segment 12, Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, Vermont
The State of New York and the six New England States of Maine, Vermont, New Hampshire, Massachusetts, Connecticut, and Rhode Island compose Segment 12 of this Atlas (fig. 1). The seven States have a total land area of about 116,000 square miles (table 1); all but a small area in southwestern New York has been glaciated. Population in the States of Segment 12 totals about 30,408,000 (table 1) and is concentrated in southern and eastern Massachusetts, Connecticut, Rhode Island, and especially New York (fig. 1). The northern part of the segment and the mountainous areas of New York and much of New Hampshire, Vermont, and Maine are sparsely populated. The percentage of population supplied from ground-water sources during 1980 was 54 to 60 percent in Maine, New Hampshire, and Vermont (table 1). Nearly all rural, domestic, and small-community water systems obtain water from wells that are, in comparison with other sources, the safest and the least expensive to install and maintain. Where water demand is great-in the urban areas of New York, Connecticut, Massachusetts, and Rhode Island-sophisticated reservoir, pipeline, and purification systems are economically feasible and are needed to meet demands. Surface water is the principal source of supply in these four States, and ground water was used to supply only 24 to 35 percent of their population during 1980 (table 1).
Connecticut, Maine, Massachusetts, New Hampshire, ↗
Ground Water Atlas of the United States: Segment 11, Delaware, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia
Segment 11 consists of the States of Delaware, Maryland, New Jersey, North Carolina, West Virginia, and the Commonwealths of Pennsylvania and Virginia. All but West Virginia border on the Atlantic Ocean or tidewater. Pennsylvania also borders on Lake Erie. Small parts of northwestern and north-central Pennsylvania drain to Lake Erie and Lake Ontario; the rest of the segment drains either to the Atlantic Ocean or the Gulf of Mexico. Major rivers include the Hudson, the Delaware, the Susquehanna, the Potomac, the Rappahannock, the James, the Chowan, the Neuse, the Tar, the Cape Fear, and the Yadkin-Peedee, all of which drain into the Atlantic Ocean, and the Ohio and its tributaries, which drain to the Gulf of Mexico. Although rivers are important sources of water supply for many cities, such as Trenton, N.J.; Philadelphia and Pittsburgh, Pa.; Baltimore, Md.; Washington, D.C.; Richmond, Va.; and Raleigh, N.C., one-fourth of the population, particularly the people who live on the Coastal Plain, depends on ground water for supply. Such cities as Camden, N.J.; Dover, Del.; Salisbury and Annapolis, Md.; Parkersburg and Weirton, W.Va.; Norfolk, Va.; and New Bern and Kinston, N.C., use ground water as a source of public supply. All the water in Segment 11 originates as precipitation. Average annual precipitation ranges from less than 36 inches in parts of Pennsylvania, Maryland, Virginia, and West Virginia to more than 80 inches in parts of southwestern North Carolina (fig. 1). In general, precipitation is greatest in mountainous areas (because water tends to condense from moisture-laden air masses as the air passes over the higher altitudes) and near the coast, where water vapor that has been evaporated from the ocean is picked up by onshore winds and falls as precipitation when it reaches the shoreline. Some of the precipitation returns to the atmosphere by evapotranspiration (evaporation plus transpiration by plants), but much of it either flows overland into streams as direct runoff or enters streams as base flow (discharge from one or more aquifers). The distribution of average annual runoff (fig. 2) is similar to the distribution of precipitation; that is, runoff is generally greatest where precipitation is greatest. Runoff rates range from more than 50 inches per year in parts of western North Carolina to less than 12 inches in parts of North Carolina, Virginia, and West Virginia. Parts of the seven following physiographic provinces are in Segment 11: the Coastal Plain, the Piedmont, the Blue Ridge, the New England, the Valley and Ridge, the Appalachian Plateaus, and the Central Lowland. The provinces generally trend northeastward (fig. 3). The northeastern terminus of the Blue Ridge Province is in south-central Pennsylvania, and the southwestern part of the New England Province, the Reading Prong, ends in east-central Pennsylvania. The topography, lithology, and water-bearing characteristics of the rocks that underlie the Blue Ridge Province and the Reading Prong are similar. Accordingly, for purposes of this study, the hydrology of the Reading Prong is discussed with that of the Blue Ridge Province. The Coastal Plain Province is a lowland that borders the Atlantic Ocean. The Coastal Plain is as much as 140 miles wide in North Carolina but narrows northeastward to New Jersey where it terminates in Segment 11 at the south shore of Raritan Bay. Although it is generally a flat, seaward-sloping lowland, this province has areas of moderately steep local relief, and its surface locally reaches altitudes of 350 feet in the southwestern part of the North Carolina Coastal Plain. The Coastal Plain mostly is underlain by semiconsolidated to unconsolidated sediments that consist of silt, clay, and sand, with some gravel and lignite. Some consolidated beds of limestone and sandstone are present. The Coastal Plain sediments range in age from Jurassic to Holocene and dip gently toward the ocean. The boundary between the Coastal Plain and the Piedmont Provinces is called the Fall Line (fig. 3) because falls and rapids commonly form where streams cross the contact between the consolidated rocks of the Piedmont (fig. 4) and the soft, semiconsolidated to unconsolidated sediments of the Coastal Plain. The increase in stream gradient at the Fall Line provided favorable locations for mills and other installations that harnessed water power during the early years of the Industrial Revolution, and on most major rivers, the Fall Line coincides with the head of navigation. The Piedmont Province is an area of varied topography that ranges from lowlands to peaks and ridges of moderate altitude and relief. The metamorphic and igneous rocks of this province range in age from Precambrian to Paleozoic and have been sheared, fractured, and folded. Included in this province, however, are sedimentary basins that formed along rifts in the Earth's crust and contain shale, sandstone, and conglomerate of early Mesozoic age, interbedded locally with basaltic lava flows and minor coal beds. The sedimentary rocks and basalt flows are intruded in places by diabase dikes and sills. The mountain belt of the Blue Ridge Province forms the northwestern margin of the Piedmont in most of Segment 11. This belt consists mostly of igneous and high-rank metamorphic rocks but also includes low-rank metamorphic rocks of late Precambrian age and small areas of sedimentary rocks of Early Cambrian age along its western margin. In this report, the Reading Prong of the New England Province, which is an upland that extends from east of the Susquehanna River in Pennsylvania northeastward into New Jersey (fig. 3), is treated as part of the Blue Ridge Province. Part of the Reading Prong in Pennsylvania and New Jersey and a small part of the Piedmont Province in northeastern New Jersey have been glaciated. Glacial deposits completely or partly fill some of the valleys, and the eroding action of the glacial ice removed some of the rock from the ridges. Thus, the glaciated parts of the province have a smoother topography and less relief than other parts. The Valley and Ridge Province is characterized by layered sedimentary rock that has been complexly folded and locally thrust faulted. As the result of repeated cycles of uplift and erosion, resistant layers of well-cemented sandstone and conglomerate form elongate mountain ridges and less resistant, easily eroded layers of limestone, dolomite, and shale form valleys. The rocks of the province range in age from Cambrian to Pennsylvanian. Parts of this province from central Pennsylvania into New Jersey have been glaciated, and glacial deposits fill or partially fill some of the valleys. The Appalachian Plateaus Province is underlain by rocks that are continuous with those of the Valley and Ridge Province, but in the Appalachian Plateaus the layered rocks are nearly flat-lying or gently tilted and warped, rather than being intensively folded and faulted. The boundary between the two provinces is a prominent southeast-facing scarp called the Allegheny Front in most of the northern part of Segment 11 (fig_ 5) and the Cumberland Escarpment in the southern part. The scarp faces the Valley and Ridge Province, and throughout most of the segment, the eastern edge of the Appalachian Plateaus Province is higher than the ridges in the Valley and Ridge. Like parts of the Reading Prong and the Valley and Ridge Province, the northern part of the Appalachian Plateaus Province in Pennsylvania has been glaciated. In the glaciated section, the surface is mantled by glacial drift, and the valleys are partly filled with glacial deposits. The northwestern corner of Segment 11 contains a small part of the Central Lowland Province. This flat lowland is underlain by gently dipping sedimentary rocks, some of which are the same geologic formations as those of the Appalachian Plateaus Province. The two provinces are separated by a northwest- facing scarp. Because of the small area of the Central Lowland Province within the segment and the similarity of aquifer properties with those of the glaciated part of the Appalachian Plateaus Province, the two provinces are discussed together in this report.
Delaware, Maryland, New Jersey, North Carolina, Pe↗
Ground Water Atlas of the United States: Segment 1, California, Nevada
California and Nevada compose Segment 1 of the Ground Water Atlas of the United States. Segment 1 is a region of pronounced physiographic and climatic contrasts. From the Cascade Mountains and the Sierra Nevada of northern California, where precipitation is abundant, to the Great Basin in Nevada and the deserts of southern California, which have the most arid environments in the United States, few regions exhibit such a diversity of topography or environment. Since the discovery of gold in the mid-1800's, California has experienced a population, industrial, and agricultural boom unrivaled by that of any other State. Water needs in California are very large, and the State leads the United States in agricultural and municipal water use. The demand for water exceeds the natural water supply in many agricultural and nearly all urban areas. As a result, water is impounded by reservoirs in areas of surplus and transported to areas of scarcity by an extensive network of aqueducts. Unlike California, which has a relative abundance of water, development in Nevada has been limited by a scarcity of recoverable freshwater. The Truckee, the Carson, the Walker, the Humboldt, and the Colorado Rivers are the only perennial streams of significance in the State. The individual basin-fill aquifers, which together compose the largest known ground-water reserves, receive little annual recharge and are easily depleted. Nevada is sparsely populated, except for the Las Vegas, the Reno-Sparks, and the Carson City areas, which rely heavily on imported water for public supplies. Although important to the economy of Nevada, agriculture has not been developed to the same degree as in California due, in large part, to a scarcity of water. Some additional ground-water development might be possible in Nevada through prudent management of the basin-fill aquifers and increased utilization of ground water in the little-developed carbonate-rock aquifers that underlie the eastern one-half of the State. The potential problem of withdrawals in excess of natural recharge, however, will require careful management of ground-water withdrawals.
California, Nevada↗
Ground Water Atlas of the United States: Segment 5, Arkansas, Louisiana, Mississippi
The States of Arkansas, Louisiana, and Mississippi, which are located adjacent to each other and north of the Gulf of Mexico, compose Segment 5 of this Atlas. The three-State area encompasses an area of nearly 149,000 square miles. These States are drained by numerous rivers and streams, such as the Atchafalaya, the Teche, the Vermilion, the Calcasieu, the Mermentau, the Sabine, the Tombigbee, the Pascagoula, the Wolf, and the Pearl Rivers, that drain directly to the Gulf of Mexico. The Yazoo, the Big Black, the Arkansas, the St. Francis, the Red, and the White Rivers are tributaries of the Mississippi River, which is the largest of the rivers that drain the three States. Although surface water is the largest source of freshwater to public supply, domestic and commercial, industrial, mining, thermoelectric power and agricultural users, ground water also is important and accounts for 38 percent of total water use in Arkansas, Louisiana, and Mississippi. Precipitation is the ultimate source of water that recharges the ma-jor aquifers in Segment 5. Average annual rainfall (1951-80) amounts range from about 40 to about 68 inches (fig. 1). Temporal (seasonal) and spatial variations in precipitation are evident in the three-State area. Average annual rainfall is greatest (60 inches per year or more) in southern Louisiana and southern Mississippi and diminishes in Arkansas and in northwestern Louisiana. Precipitation is greatest during January and May in Arkansas. May to September represent the wettest months in southeastern Louisiana and southern Mississippi. March and April are the wettest months in northern Mississippi. Average annual (1951-80) runoff ranges from less than 12 inches in western Louisiana and northwestern Arkansas to more than 20 inches in southern and northern Mississippi and in central and western Arkansas (fig. 2). Comparison of precipitation and runoff maps shows that less than one-half of the annual precipitation leaves the area as stream runoff. Much of the water that does not exit Segment 5 as runoff is returned to the atmosphere by evapotranspiration, which is the combination of transpiration by vegetation and evaporation from marshes, swamps, lakes and streams. A small amount of water recharges aquifers that are either exposed or buried to shallow depths, and an even smaller amount percolates downward and enters the deep flow system.
Arkansas, Louisiana, Mississippi↗
Ground Water Atlas of the United States: Segment 7, Idaho, Oregon, Washington
The States of Idaho, Oregon, and Washington, which total 248,730 square miles, compose Segment 7 of this Atlas. The area is geologically and topographically diverse and contains a wealth of scenic beauty, natural resources, and ground and surface water that generally are suitable for all uses. Most of the area of Segment 7 is drained by the Columbia River, its tributaries, and other streams that discharge to the Pacific Ocean. Exceptions are those streams that flow to closed basins in southeastern Oregon and northern Nevada and to the Great Salt Lake in northern Utah. The Columbia River is one of the largest rivers in the Nation. The downstream reach of the Columbia River forms most of the border between Oregon and Washington. In 1990, Idaho, Oregon, and Washington had populations of 1.0 million, 2.8 million, and 4.9 million, respectively. The more densely populated parts are in lowland areas and stream valleys. Many of the mountains, the deserts, and the upland areas of Idaho, Oregon, and Washington lack major population centers. Large areas of Idaho and Oregon are uninhabited and are mostly public land (fig. 1) where extensive ground-water development is restricted. Surface water is abundant in Idaho, Oregon, and Washington, though not always available when and where needed. In some places, surface water provides much of the water used for public-supply, domestic and commercial, agricultural (primarily irrigation and livestock watering), and industrial purposes. In arid parts of Segment 7, however, surface water has long been fully appropriated, chiefly for irrigation. Ground water is used when and where surface-water supplies are lacking. Ground water is commonly available to shallow wells that are completed in unconsolidated-deposit aquifers that consist primarily of sand and gravel but contain variable quantities of clay and silt. Many large-yield public-supply and irrigation wells and thousands of domestic wells are completed in these types of aquifers, generally in areas of privately owned land (fig. 1). In many places, deeper wells produce water from underlying volcanic rocks, usually basalt. Most irrigation (fig. 2) is on lowlands next to streams and on adjacent terraces. Generally, lowlands within a few miles of a main stream are irrigated with surface water diverted by gravity flow from the main stream or a reservoir and distributed through a system of canals and ditches. In some areas, water is pumped to irrigate lands farther from the stream at a higher altitude. Along the Snake and Columbia Rivers, large pumping systems withdraw billions of gallons of water per day from the rivers to irrigate adjacent uplands that are more than 500 feet higher than the rivers. Elsewhere, irrigation water is obtained from large-capacity wells, where depth to water might exceed 500 feet below land surface. Aquifers in Idaho, Oregon, and Washington, as in most other States, differ considerably in thickness and permeability, and well yields differ accordingly. Ground-water levels in a few areas have declined as a result of withdrawals by wells. State governments have taken steps to alleviate declines in some areas by enacting programs that either limit the number of additional wells that can be completed in a particular aquifer (Ground-Water Management Area) or prevent further ground-water development (Critical Ground-Water Area). Segment 7 includes some of the driest parts of the Nation, as well as some of the wettest. Average annual precipitation (1951-80) ranges from less than 10 inches in arid parts of Idaho, Oregon, and Washington to more than 80 inches in the western parts of Oregon and Washington (fig. 3). Most storms generally move eastward through the area. The eastward-moving air absorbs the moisture that evaporates from the Pacific Ocean. As this air encounters the fronts of mountain ranges, it rises, cools, and condenses. Accordingly, the western sides of the mountain ranges receive the most precipitation. Much of the annual precipitation moves directly to streams as overland runoff. Some of the precipitation is returned to the atmosphere by evapotranspiration, which is the combination of evaporation from the surface and transpiration from the plants. A small part of the precipitation infiltrates the soil and percolates downward to recharge underlying aquifers. Average annual runoff ( 1951-80) in the segment varies considerably (fig. 4), and the distribution of the runoff generally parallels that of precipitation. In the arid and the semiarid parts of Segment 7, most precipitation replenishes soil moisture, evaporates, or is transpired by vegetation. Little is left to maintain streamflow or to recharge aquifers. In the wetter parts, much of the precipitation runs off the land surface to maintain streamflow, and because evaporation is usually less in wetter areas, more water is available to recharge aquifers. Precipitation that falls as snow generally does not become runoff until spring thaws begin. Reservoirs constructed on major streams to mitigate flooding and to store water for irrigation, hydroelectric-power generation, and recreation also affect the timing of runoff. The runoff is stored and subsequently released during drier periods to maintain downstream flow.
Idaho, Oregon, Washington↗
Ground Water Atlas of the United States: Segment 8, Montana, North Dakota, South Dakota, Wyoming
The States of Montana, North Dakota, South Dakota, and Wyoming compose the 392,764-square-mile area of Segment 8, which is in the north-central part of the continental United States. The area varies topographically from the high rugged mountain ranges of the Rocky Mountains in western Montana and Wyoming to the gently undulating surface of the Central Lowland in eastern North Dakota and South Dakota (fig. 1). The Black Hills in southwestern South Dakota and northeastern Wyoming interrupt the uniformity of the intervening Great Plains. Segment 8 spans the Continental Divide, which is the drainage divide that separates streams that generally flow westward from those that generally flow eastward. The area of Segment 8 is drained by the following major rivers or river systems: the Green River drains southward to join the Colorado River, which ultimately discharges to the Gulf of California; the Clark Fork and the Kootenai Rivers drain generally westward by way of the Columbia River to discharge to the Pacific Ocean; the Missouri River system and the North Platte River drain eastward and southeastward to the Mississippi River, which discharges to the Gulf of Mexico; and the Red River of the North and the Souris River drain northward through Lake Winnipeg to ultimately discharge to Hudson Bay in Canada. These rivers and their tributaries are an important source of water for public-supply, domestic and commercial, agricultural, and industrial uses. Much of the surface water has long been appropriated for agricultural use, primarily irrigation, and for compliance with downstream water pacts. Reservoirs store some of the surface water for flood control, irrigation, power generation, and recreational purposes. Surface water is not always available when and where it is needed, and ground water is the only other source of supply. Ground water is obtained primarily from wells completed in unconsolidated-deposit aquifers that consist mostly of sand and gravel, and from wells completed in semi-consolidated- and consolidated-rock aquifers, chiefly sandstone and limestone. Some wells withdraw water from volcanic rocks, igneous and metamorphic rocks, or fractured fine-grained sedimentary rocks, such as shale; however, wells completed in these types of rocks generally yield only small volumes of water. Most wells in the four-State area of Segment 8 are on privately owned land (fig. 2). Agriculture, primarily irrigation, is one of the largest uses of ground water. The irrigation generally is on lowlands close to streams (fig. 3). Lowlands within a few miles of major streams usually are irrigated with surface water that is diverted by gravity flow from the main stream or a reservoir and transported through a canal system. Surface water also is pumped to irrigate land that gravity systems cannot supply. In addition, ground water is pumped from large-capacity wells to supplement surface water during times of drought or during seasons of the year when surface water is in short supply. Ground water is the only source of water for irrigation in much of the segment. The thickness and permeability of aquifers in the area of Segment 8 vary considerably, as do yields of wells completed in the aquifers. Ground-water levels and artesian pressures (hydraulic head) have declined significantly in some places as a result of excessive withdrawals by wells. State governments have taken steps to control the declines by enacting programs that either limit the number of additional wells that can be completed in a particular aquifer or prevent further ground-water development altogether. The demand for water is directly related to the distribution of people. In 1990, Montana had a population of 799,065; North Dakota, 638,800; South Dakota, 696,004; and Wyoming, 453,588. The more densely populated areas are on lowlands near major streams. Many of the mountain, desert, and upland areas lack major population centers, particularly in Montana and Wyoming, where use of much of the land is controlled by the Federal Government and withdrawal of ground water is restricted. Average annual precipitation (1951-80) in Segment 8 ranges from less than 8 inches in parts of Montana and Wyoming to more than 40 inches in some of the mountainous areas (fig. 4). Most storms move eastward through Segment 8 and are particularly common during the winter months. Moisture that evaporates from the Pacific Ocean is absorbed by eastward- moving air. As the moisture-laden air masses move eastward, they rise and cool as they encounter mountain ranges and lose some of their moisture to condensation. Consequently, the western sides of mountain ranges receive the most precipitation, much of it as snow during the winter months. In contrast, the eastern sides of some of the higher mountain ranges are in rain shadows and receive little precipitation. East of the Continental Divide, precipitation that falls during many summer storms results from northward-moving, moisture-laden air masses from the Gulf of Mexico. These air masses move northward when the polar front recedes; accordingly, a major part of the annual precipitation falls on the plains during the growing season. Average annual precipitation minus the total of average annual runoff plus evapotranspiration (the combination of evaporation and transpiration by plants) is the amount of water potentially available for recharge to the aquifers. Average annual runoff (1951-80) in the area of Segment 8 varies greatly, and the distribution of runoff (fig. 5) generally parallels that of precipitation. In arid and semiarid areas of the segment, most precipitation replenishes soil moisture, evaporates, or is transpired by vegetation, and only a small part of the precipitation is left to maintain streamflow or recharge aquifers. In wetter areas of the segment, much of the precipitation runs off the land surface directly to perennial streams. Because a smaller percentage of precipitation in wet areas usually is lost to evapotranspiration than in dry areas, more water is, therefore, available to recharge aquifers where more precipitation falls. Precipitation that falls as snow generally does not become runoff until spring thaws begin. Runoff is affected in some areas by reservoirs that have been constructed on major streams to mitigate flooding and to store water for irrigation, electrical power generation, and recreation. Water stored in reservoirs during times when runoff is great is subsequently released during drier periods to maintain downstream flow.
Montana, North Dakota, South Dakota, Wyoming↗